1. Field of the Invention
The invention is in the field of manufacturing a lactulose powder. Particularly, the invention relates to a method for manufacturing a highly purified lactulose powder less hygroscopic than that obtained by any methods of prior art.
2. Description of the Prior Art
Trials have been carried out for several decades in the past with an object of separating purified lactulose from a syrup containing lactulose by crystallization. For example, Montgomery et al. (Journal of the American Chemical Society, 52, 2101, 1930), Whistler et al., ("Methods in Carbohydrate Chemistry," edited by Whistler et al., Volume 1, Page 325, Academic Press, New York and London, 1962) and Adachi Nyugikyo Shiryo (Bulletin of Japan Dairy Technical Association), Volume 22, No. 2, Page 3, 1972) gave detailed description. However, these methods have a drawback that they cannot be put into practice use industrially despite of their effectiveness as experimental methods because of their complexity and the use of methyl alcohol which is toxic to human and which cannot be removed absolutely . Further, there are no prior arts of using only ethyl alcohol in the treatment of lactulose syrups or lactulose powders, because pure lactulose crystals cannot be obtained by adding ethyl alcohol to a syrup containing lactulose differing from the case of adding methyl alcohol. Therefore, a drying method using lactulose syrups has been carried out hitherto industrially instead of the crystallization method considering the difficulties in the crystallization of lactulose. As for the methods for manufacturing a lactulose-containing powder from a lactulose syrup with a higher content of lactulose, several methods are known at the present time. They are, for instance, a method of spray-drying of the syrup as it is regardless of the yield, a drying method up of the syrup admixed with a drying aid such as a grain flour (Japanese Patent Publication Gazette No. 861/65), konjak powder (Japanese Patent Publication Gazette No. 44331/74) or a protein (Japanese Patent Publication Gazette No. 44332/74) and a method of freeze-drying of the syrup (Japanese Patent Publication Gazette No. 54556/74).
However, there is an inconvenience that the grain flour, the konjak powder or the protein is included in the powder as the final product in the manufacturing by the methods using a drying aid as described in the above. The methods without use of any drying aid have some drawbacks such as the decrease of the yield and the increase of the manufacturing cost. Further, the powders containing lactulose obtained by any of the above-mentioned methods have a drawback that they are so highly hygroscopic that are apt to agglomerate by absorbing moisture in an ambience of room temperature and of ordinary humidity despite of the low content of moisture in the powders. Therefore, there is an inconvenience that treatment in a room with a low humidity is required in packaging of the powders or in tablet-forming of the powders prepared by these methods, and further, there are some difficulties in the preservation and in the packaging for the storing over a long term due to the high hygroscopicity.